Same here (UK). The solution is to go in via a US-sited proxy-server, of which there are many and I've no idea which is the best. Try pasting the link into http://www.hidemyass.com/proxy/ That works for me.

Well, I sewed all 39 pages together as you said using a trial copy of a program called 'pdfFactory'. If you would like to have it (ie the complete key), just let me know.

One interesting point: lesson 1 in the key is lesson 24 in the coursebook, lesson 2 in the key is lesson 25 in the coursebook, and so on. Otherwise only very minor discrepancies between the sentences. But there must have been another 'Introduction to Latin Composition' by Allen out there once upon a time that matched the key. I wonder where that one is...?

So that's where it was. Great! I've ordered an electronic copy from KirtasBooks.com (easier than downloading and sewing pages).

Perhaps the 1881 key too will surface eventually.

Off topic(?): Since you're such a great textbook detective, I wonder if you might be able to locate a related kind of 'untraceable' entity - basic data concerning a textbook author? Earlier this year I tried to get a library to make an electronic copy of a Greek textbook by Francis Ritchie (of Fabulae Faciles fame) but I was told the author had to have been dead for a given number of years (even though the book was obviously public domain). I could find neither his birth nor death date anywhere despite his erstwhile star status. It seems some names really are written in water. Or was I looking in the wrong place?